This study will evaluate the consistency of the immune response to three different lots of GSK Biologicals' trivalent investigational MMR vaccine (NV_MMR) and compare its immunogenicity to the US standard of care comparator vaccine M-M-R II, Merck and Co., Inc. (COM_MMR) in children during their second year of life.

The INV_MMR vaccine will be given as one of three consistency lots manufactured to target potencies designated as INV_MMR_L1, INV_MMR_L2 and INV_MMR_L3.

The COM_MMR vaccine will be given as one of two lots designated COM_MMR_L1 and COM_MMR_L2 and will be analysed as pooled lots within the study.

The MMR vaccine will be co-administered with Varivax (VV), Havrix (HAV) and (in the US sub-cohort only) Prevnar 13 (PCV-13) which are routinely administered to children of this age in the US.